The present invention relates in general to photofinishing systems and is particularly directed to a device (kit) and method which allows simple calibration of a photofinishing system printer.
Photofinishers customarily employ one or more quality control tools, typically in the form of either reference first or second generation original developed negatives. xe2x80x9cFirst generationxe2x80x9d and xe2x80x9csecond generationxe2x80x9d original negatives are described in U.S. Pat. No. 5,223,891 and U.S. Pat. No. 5,313,251. These developed reference images frequently consist of human portrait images and reference color or neutral gray patches. Photofinishers have typically calibrated their printers by printing these developed negatives, measuring the densities of reference patches on the resulting prints using a densitometer, and adjusting printer calibration controls until the densities of the reference patches reach recommended (desired) values.
Originally, these reference images were camera originals (that is, first generation originals) and were specified to extremely high standards. Because of these high standards, the production of them was time consuming, labor intensive and expensive. The adoption of second generation originals as control tools (as disclosed in U.S. Pat. No. 5,223,891 and U.S. Pat. No. 5,313,251), helped to address the above issues and also facilitated:
a. Identical images on multiple copies of a reference developed film strip.
b. Higher standards of sensitometric uniformity between multiple copies of a reference developed film strip.
The calibration of printers using second generation originals was still generally achieved by measuring the reflection densities of a calibration patch in the image and comparing those densities to specified aim densities provided with the control tool. A less formal method of calibration involved repeatedly printing the image after adjustment of the printer balance until a pleasing result, possibly matching a single reference print, is obtained.
However, the previously used methods have a number of disadvantages. First, if the desired result is not obtained when the reference images are printed, there is no indication of how the printer should then be adjusted to obtain the desired result Adjustments are usually made by trial and error, the number of trials required depending on the experience and color discrimination of the operator. Second, if calibration is achieved by visual matching to a supplied reference print, that reference print is the only available aim reference available. This aim may not reflect the color balance or density desired by the photofinisher. Third, if calibration is achieved by densitometric measurements of a calibration patch, while that patch can be adjusted perfectly there is a trade off in obtaining the desired rendering of the calibration patch (such as a typical gray patch) compared to other important colors in the scene. Fourth, because processed negatives were used, this method of calibration failed to take account of any bias or offset in the film processing components (that is, the physical and chemical components of the film developing process) between the film process used by the calibration kit manufacturer to develop the reference film strip and the film processing components used by the photofinisher to develop customer negatives from a customer film strip.
The present invention, then, provides an apparatus for calibrating a printer of a photofitishing system, comprising:
(a) a reference film strip carrying at least one reference image;
(b) a reference chart carrying multiple renderings of the reference image representing different printer exposures; and
c) a substrate carrying printer correction factors needed to change a photographic print obtained from the reference image on the reference film strip, to match any desired rendering on the reference chart.
The present invention further provides a method of making a reference chart useful in the above apparatus, and a method of calibrating a printer of a photofinishing system using the apparatus.
The apparatus and method of the present invention can provide a number of advantages. First, when a desired rendering is not obtained when the reference images are printed, the apparatus provides a quantitative indication of how the printer should then be adjusted to obtain the desired rendering. Second, a large number of different color balances and density renderings can be available on the reference chart and the photofinisher may select any one of these as his desired aim. Third, because calibration is primarily achieved by visually matching an ideal compromise between balance and density of all important elements in the reference scene can be more easily achieved. Fourth, because unprocessed negatives are used, the method of the present invention takes account of any bias or offset in the film processing components of the photofinisher.